CERN has discovered another clue to the mystery of the disappeared antimatter in the Universe
(ORDO NEWS) — This is one of the greatest mysteries of physics. All the particles that make up the matter around us – electrons and protons – have versions of antimatter that are nearly identical, but with specular properties, such as the opposite electrical charge.
When antimatter and a particle of matter meet, they annihilate in a burst of energy.
If antimatter and matter are indeed identical, but mirror images of each other, they should have been produced in equal quantities during the Big Bang. The problem is that it would destroy everything. But today there is almost no antimatter left in the Universe – it appears only in some radioactive decays and in a small part of cosmic rays.
So what happened to him? Using the LHCb experiment at CERN to study the difference between matter and antimatter, we discovered a new way of making this difference.
The existence of antimatter was predicted by the physicist Paul Dirac’s equation describing the motion of electrons in 1928. It was unclear at first if this was just a mathematical quirk or a description of a real particle.
But in 1932, Karl Anderson discovered antimatter, the electron’s partner, the positron, in the study of cosmic rays falling on Earth from space. Over the next several decades, physicists discovered that all particles of matter have antimatter partners.
Scientists believe that in a very hot and dense state, shortly after the Big Bang, processes should have occurred in which matter preferred antimatter. This created a slight excess of matter, and when the universe cooled down, all of the antimatter was destroyed or annihilated by an equal amount of matter, leaving a tiny excess of matter.
And it is this excess that makes up everything that we see in the universe today.
It is unclear exactly what processes led to the surplus, and physicists have been watching this closely for decades.
The behavior of quarks, which are the fundamental building blocks of matter along with leptons, can shed light on the difference between matter and antimatter. Quarks come in many different kinds or “flavors” known as top, bottom, charming, odd, diligent, and true, plus six matching antiquarks.
The up and down quarks are what make up the protons and neutrons in the nuclei of ordinary matter, and other quarks can be formed by high-energy processes – for example, when particles collide in accelerators such as the Large Hadron Collider at CERN.
Particles made up of a quark and an antiquark are called mesons, and there are four neutral mesons (B0S, B0, D0, and K0) that exhibit exciting behavior. They can spontaneously transform into their antiparticle partner, and then back again – a phenomenon that was first observed in 1960.
Because they are unstable, they will “decay” – fall apart – into other more stable particles at some point during their oscillation. This decay for mesons occurs somewhat differently than for antimesons, which, combined with oscillation, means that the decay rate varies with time.
The rules for vibrations and decays are given by a theoretical framework called the Cabibbo-Kobayashi-Maskawa Mechanism (CKM). He predicts that there is a difference in the behavior of matter and antimatter, but it is too small to generate the excess of matter in the early universe needed to explain the abundance we see today.
This indicates that there is something we do not understand, and that studying this topic may call into question some of our most fundamental theories in physics.
New physics?
Our recent result of the LHCb experiment is the study of neutral B0S mesons, the study of their decays into pairs of charged K mesons. B0S mesons were created by colliding protons with other protons at the Large Hadron Collider, where they oscillated in their anti-season and bounced back three trillion times per second. The collisions also created anti-B0S mesons that oscillate in the same way, giving us samples of mesons and antimesons that we could compare.
We counted the number of decays in the two samples and compared the two numbers to see how this difference changed as the fluctuations developed. There was a slight difference – more decays occurred for one of the B0S mesons. And for the first time for B0S mesons, we noticed that the difference in decay or asymmetry changes depending on the vibrations between the B0S meson and the antimeson.
In addition to being an important milestone in the study of the difference between matter and antimatter, we were also able to measure the size of asymmetries. This can be translated into measurements of several parameters of the underlying theory.
Comparing results with other measurements provides a consistency check as to whether the currently accepted theory is a correct description of nature. Since the slight preference for matter over antimatter that we observe on a microscopic scale cannot explain the overwhelming abundance of matter that we observe in the universe, it is likely that our current understanding is an approximation of a more fundamental theory.
Examining this mechanism, which we know can generate an asymmetry of matter and antimatter by examining it from different angles, can tell us what the problem is. Exploring the world at the smallest scale is our best chance to understand what we see at the largest scale.
Lars Eklund, Professor of Particle Physics, University of Glasgow.
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